Electrical effects of acidification in the rabbit proximal convoluted tubule.

The electrical characteristics of acidification were examined in isolated rabbit proximal convoluted tubules (PCT). In PCT perfused and bathed with an ultrafiltrate-like solution, the transepithelial potential difference due to active transport (transport PD) averaged -2.4 mV. The transport PD shifted in a negative direction by 1 mV (to -3.4 mV) when carbonic anhydrase inhibitors were added to the bath solution, and in a positive direction by 1.4 mV (to -1.0 mV) when bath sodium bicarbonate concentration was lowered. The positive shift was prevented by addition of either carbonic anhydrase inhibitors or the anion transport inhibitor SITS to the bath. These findings suggested electrogenic acidification. However, when electrogenic sodium transport was inhibited by removal of glucose and alanine from the luminal fluid, a positive PD suggesting electrogenic acidification was not observed. In tubules lacking glucose and alanine in the luminal fluid the rate of total CO2 absorption was 97.2 before and 35.4 pmol.mm-1.min-1 after inhibition of carbonic anhydrase. These findings do not support an independent electronic acidification mechanism. Nonelectrogenic acidification may secondarily after transepithelial PD by changes in transcellular current flow or by changes in paracellular resistance.